Silicon (Si) Materials, Optical Materials, Optical Grade Materials

Silicon is used as an optical window primarily in the 3 to 5 micron band and as a substrate for production of optical filters. Large blocks of Silicon with polished faces are also employed as neutron targets in Physics experiments.

Silicon (Si) Material, Optical Material, Optical Grade Material

Transmission Range :	1.2 to 15 μm (1)
Refractive Index :	3.4223 @ 5 μm (1) (2)
Reflection Loss :	46.2% at 5 μm (2 surfaces)
Absorption Coefficient :	0.01 cm^-1 at 3 μm
Reststrahlen Peak :	n/a
dn/dT :	160 x 10^-6 /°C (3)
dn/dμ = 0 :	10.4 μm
Density :	2.33 g/cc
Melting Point :	1420 °C
Thermal Conductivity :	163.3 W m^-1 K^-1 at 273 K
Thermal Expansion :	2.6 x 10^-6 / at 20°C
Hardness :	Knoop 1150
Specific Heat Capacity :	703 J Kg^-1 K^-1
Dielectric Constant :	13 at 10 GHz
Youngs Modulus (E) :	131 GPa (4)
Shear Modulus (G) :	79.9 GPa (4)
Bulk Modulus (K) :	102 GPa
Elastic Coefficients :	C₁₁=167; C₁₂=65; C₄₄=80 (4)
Apparent Elastic Limit :	124.1MPa (18000 psi)
Poisson Ratio :	0.266 (4)
Solubility :	Insoluble in Water
Molecular Weight :	28.09
Class/Structure :	Cubic diamond, Fd3m

Refractive Index and Optical Transmittance curve----

Refractive Index(No=Ordinary Ray):

µm	No	µm	No	µm	No
1.357	3.4975	1.367	3.4962	1.395	3.4929
1.5295	3.4795	1.660	3.4696	1.709	3.4664
1.813	3.4608	1.970	3.4537	2.153	3.4476
2.325	3.4430	2.714	3.4358	3.000	3.4320
3.303	3.430	3.500	3.4284	4.000	3.4257
4.258	3.4245	4.500	3.4236	5.000	3.4223
5.500	3.4213	6.000	3.4202	6.500	3.4195
7.000	3.4189	7.500	3.4186	8.000	3.4184
8.500	3.4182	10.00	3.4179	10.50	3.4178
11.04	3.4176

Optical Transmittance Curve of Si (Reference Data):

With one of the lowest densities of the common IR materials, it is ideal for systems with weight constraints.

It is harder than Ge and not as brittle.

It is the lowest material cost option of all the IR materials.

Si is diamond turnable.

Typeical application:Thermal imaging, FLIR.

Products manufactured:Lenses, Aspheric Lenses, Binary(Diffractive) Lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges.

Surface finish:Typical specifications for surface quality in the infrared are a 40-20 scratch dig in the 1.2 to 3μm spectral region and 60-40 scratch-dig for the 3-7μm area. Diamond Turned surface finishes of 120Angstroms rms or better are typical.

Surface figureIn the infrared, typical required surface figure ranges from 1/2 wave to 2 waves @0.6328μm and are usually specified depending on the system performance requirements.

AR coating options:In the infrared, typical required surface figure ranges from 1/2 wave to 2 waves @0.6328μm and are usually specified depending on the system performance requirements.

Product Notes:------------ --------------------------------------

Silicon is grown by Czochralski pulling techniques (CZ) and contains some oxygen which causes an absorption band at 9 microns. To avoid this, Silicon can be prepared by a Float-Zone (FZ) process. Optical Silicon is generally lightly doped ( 5 to 40 ohm cm) for best transmission above 10 microns. Silicon has a further pass band 30 to 100 microns which is effective only in very high resistivity uncompensated material. Doping is usually Boron (p-type) and Phosphorus (n-type).
REFERENCES:
(1) Handbook Optical Constants, ed Palik, V1, ISBN 0-12-544420-6
(2) Li, Refractive Index of Germanium etc, J.Phys Chem, V9, p561, 1980
(3) Icenogle et al, Appl. Opt. V15, 2348 (1976)
(4) Wortman & Evans, V36, (1), P153 (1965)

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Data provided is extracted from our technical handbook of materials. While every attempt has been made to verify the source of the information, ultiQuest Technology accept no responsibility for accuracy of data

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